The present invention relates to a picture converting apparatus, a picture converting method, a learning apparatus, a learning method, and a record medium, in particular, to those for generating a compressed picture from which an original picture can be restored.
The inventor of the present invention has proposed a technology for generating a high resolution picture using a low resolution picture as disclosed in Japanese Patent Laid Open Publication No. 10-93980. According to the related art reference, using a low resolution picture of which a high resolution original picture is reduced, almost the same high resolution picture as the original picture can be restored. In the related art reference, as shown in FIG. 1, the pixel values of (3xc3x973) pixels a to i that surround a pixel i of a high resolution picture (a restored picture) at the position corresponding to a considered pixel I of a low resolution picture (an upper hierarchical level picture) are obtained by calculating linear combinations of a plurality of pixels (for example, (3xc3x973) pixels A to I) of the low resolution picture at the positions adjacent thereto and predetermined predictive coefficients. In addition, errors between the pixel values of the restored picture and the pixel values of the original picture are calculated. Corresponding to the calculated results, the pixel values of the low resolution picture and the predictive coefficients are repeatedly updated.
Conventionally, the pixel values of a low resolution picture are updated under the condition that the pixel values of pixels adjacent to each pixel are fixed. In other words, as shown in FIG. 1, the pixel value of the considered pixel I of the low resolution picture is updated to an optimal value under the condition that the pixel values of the eight pixels A to H that surround the considered pixel I and the values of the predetermined predictive coefficients are fixed.
Thus, after the pixel value of the pixel I is updated, if the pixel value of the pixel D is updated, since the pixel D is a pixel whose pixel value was fixed when the pixel value of the pixel I was updated, the pixel value of the pixel I that was updated is not optimum to the updated pixel D. Thus, when the pixel value of each pixel of the low resolution picture (an upper hierarchical level picture) is successively updated, the resultant low resolution picture (an upper hierarchical level picture) of which all the pixel values were finally updated is not always an optimum picture of which the original picture can be restored.
Although this problem can be solved by simultaneously updating the pixel values of a plurality of adjacent pixels of the low resolution picture (un upper hierarchical level picture) to optimum values, the number of calculations becomes huge. Thus, it takes a long time to perform such calculations. In addition, the scale of the calculating circuit becomes large. Consequently, such a method is substantially impossible.
The present invention is made from the above-mentioned point of view. An object of the present invention is to obtain a low resolution picture of which a high resolution picture almost similar to an original picture can be restored in a short time in such a manner that the pixel values of a plurality of adjacent pixels are simultaneously updated.
The invention of claim 1 is a picture data converting apparatus for converting first picture data into second picture data whose picture quality is lower than the first picture data, comprising:
an intermediate picture data generating portion for generating intermediate picture data whose picture quality is almost the same as the second picture data from the first picture data;
a storing portion for storing the intermediate picture data;
a block extracting portion for extracting a plurality of pixel data for each block which is part of one screen from the intermediate picture data;
a predictive coefficient generating portion for outputting generated or pre-obtained predictive coefficients;
a pixel value updating portion for updating the pixel values of the pixels of the intermediate picture data extracted by the block extracting portion according to the predictive coefficients, the intermediate picture data, and the first picture data;
a predictive picture data generating portion for generating predictive picture data whose picture quality is almost the same as the first picture data according to the intermediate picture data whose pixel values are updated by the pixel value updating portion and the predictive coefficients;
an error detecting portion for detecting an error between the first picture data and the predictive picture data; and
a controlling portion for deciding whether or not the intermediate picture data is used as an output picture according to the error.
The invention of claim 6 is a picture data converting method for converting first picture data into second picture data whose picture quality is lower than the first picture data, comprising the steps of:
generating intermediate picture data whose picture quality is almost the same as the second picture data from the first picture data;
extracting a plurality of pixel data for each block which is part of one screen from the intermediate picture data;
outputting generated or pre-obtained predictive coefficients;
updating the pixel values of the pixels of the intermediate picture data extracted at the block extracting portion according to the predictive coefficients, the intermediate picture data, and the first picture data;
generating predictive picture data whose picture quality is almost the same as the first picture data according to the intermediate picture data whose pixel values are updated and the predictive coefficients;
detecting an error between the first picture data and the predictive picture data; and
deciding whether or not the intermediate picture data is used as an output picture according to the error.
The invention of claim 11 is a learning apparatus for learning pixel values of second picture data when converting first picture data into the second picture data whose picture quality is lower than the first picture data, comprising:
an intermediate picture data generating portion for generating intermediate picture data whose picture quality is almost the same as the second picture data from the first picture data;
a storing portion for storing the intermediate picture data;
a block extracting portion for extracting a plurality of pixel data for each block which is part of one screen from the intermediate picture data;
a predictive coefficient generating portion for outputting generated or pre-obtained predictive coefficients;
a pixel value updating portion for updating the pixel values of the intermediate picture data extracted by the block extracting portion according to the predictive coefficients, the intermediate picture data, and the first picture data;
a predictive picture data generating portion for generating predictive picture data whose picture quality is almost the same as the first picture data according to the intermediate picture data whose pixel values are updated by the pixel value updating portion and the predictive coefficients;
an error detecting portion for detecting an error between the first picture data and the predictive picture data; and
a controlling portion for deciding whether or not the intermediate picture data is used as an output picture according to the error.
wherein the pixel value updating portion updates the pixel values of the intermediate picture data using the method of least squares with the predictive coefficients as student data and the first pixel data corresponding thereto as teacher data.
The invention of claim 12 is a learning method for learning the pixel values of second picture data when converting first picture data into the second picture data whose picture quality is lower than the first picture data, comprising the steps of:
generating intermediate picture data whose picture quality is almost the same as the second picture data from the first picture data;
extracting data of a plurality of pixel data for each block which is part of one screen from the intermediate picture data;
outputting generated or pre-obtained predictive coefficients;
updating the pixel values of the extracted intermediate picture data according to the predictive coefficients, the intermediate picture data, and the first picture data;
generating predictive picture data whose picture quality is almost the same as the first picture data according to the intermediate picture data whose pixel values are updated and the predictive coefficients;
detecting an error between the first picture data and the predictive picture data; and
deciding whether or not the intermediate picture data is used as an output picture according to the error,
wherein the step for updating pixel value is performed by updating the pixel values of the intermediate picture data using the method of least squares with the predictive coefficients as student data and the first pixel data corresponding thereto as teacher data.
The invention of claim 13 is a record medium on which a computer controllable program for converting first picture data into second picture data whose picture quality is lower than the first picture data is recorded, the program comprising the steps of:
generating intermediate picture data whose picture quality is almost the same as the second picture data from the first picture data;
extracting a plurality of pixel data for each block which is part of one screen from the intermediate picture data;
generating predictive coefficients according to the extracted intermediate picture and the first picture data at the position corresponding thereto;
updating the pixel values of the extracted intermediate picture data according to the predictive coefficients, the intermediate picture data, and the first picture data;
generating predictive picture data whose picture quality is almost the same as the first picture data according to the intermediate picture data whose pixel values are updated and the predictive coefficients;
detecting an error between the first picture data and the predictive picture data; and
deciding whether or not the intermediate picture data is used as an output picture according to the error.